1. Field of the Invention
This invention relates to a helical blade type fluid compressor for compressing a fluid such as a coolant gas in a refrigerating cycle.
2. Description of the Prior Art
Compressors are usually classified into a reciprocation type and a rotary type. In addition to these two types, there are helical blade type compressors, which successively move a coolant from the suction side of a cylinder toward the discharge side thereof through work chambers to compress the coolant, and discharges the compressed coolant outside.
FIG. 1 shows an example of a conventional helical blade compressor.
In the Figure, the compressor comprises drive means including a stator 101 and a rotor 103, a cylinder 105 rotated by the drive means, and a rotary rod 109 rotated by the cylinder 105 through an oldham ring 107. The rotary rod 109 is eccentric to the cylinder 105 by a distance of "e," and therefore, turnable relative to the cylinder 105 through the oldham ring 107.
A helical groove 111 is formed around the rotary rod 109 substantially over the whole length of the rotary rod 109. A helical blade 113 is movably fitted into the groove 111. The periphery of the blade 113 is In contact with the inner face of the cylinder 105. The blade 113 turns together with the rotary rod 109.
The rotary rod 109 rotates at the eccentric position relative to the cylinder 105, to produce a relative velocity between the periphery of the rotary rod 109 and the inner face of the cylinder 105. This relative velocity changes at a period of one turn. Accordingly, the blade 113 moves inwardly and outwardly in the groove 111.
The blade 113 defines a plurality of work chambers 115 between the rotary rod 109 and the cylinder 105 along the rotary rod 109. The volume of each work chamber 115 is determined by a corresponding pitch P of the helical groove 111 to which the blade 113 is fitted as shown in FIG. 2. The pitches of the groove 111 gradually shorten from the suction side of the rotary rod 109 toward the discharge side thereof. Namely, the volumes of the work chambers 115 defined by the blade 113 gradually decrease from the suction side of the rotary rod 109 adjacent to a suction pipe 117 toward the discharge side thereof adjacent to a discharge pipe 119, so that the coolant is gradually compressed and conveyed from the suction side toward the discharge side.
In this way, a configuration of the blade 113, rotary rod 109, and cylinder 105 determines the volumes of the work chambers 115, and a suction pressure determines a discharge pressure.
The conventional helical blade fluid compressor is operated on the basis of a predetermined discharge pressure. If an excessively large or small volume of coolant is fed into the work chambers 115, the compressor cannot deal with it and causes excessive or insufficient compression. The excessive compression, in particular, causes large load to adversely affect the drive means and blade, thereby lowering reliability.
If oil, or liquid coolant is drawn into the work chambers 115, it will cause an excessively high pressure in the work chambers 115 on the discharge side, to produce excessive load to break the drive means and blade.